New Zealand is experiencing its biggest gain in net migration for four years, which will put more pressure on already rapidly rising house prices in regions such as Auckland and Christchurch.

Some economists warn that rising migration may add to the "hysteria" about house prices in Auckland, while others said people buying homes in Auckland should be aware prices could just as easily drop 10 per cent because they were so over-valued.

The BNZ said rising net migration might fuel an "already excited" housing market in some parts of the country, like Auckland.

"Is it [stronger migration] a reason for house prices to be that high and keep going up? Probably not but it just comes at a bad time," BNZ senior economist Craig Ebert said.

The Reserve Bank had flagged the rising levels of migration in recent months and as the numbers pushed higher, they would come on to the Reserve Bank's radar, Ebert said.

"This [migration] may prod the Reserve Bank on interest rates.

"It could be the cause for them to move on interest rates, sooner rather than later," he said.

Statistics New Zealand figures out yesterday showed that overall, 2300 more people arrived to stay here long-term, than left the country in June alone.

That was the highest monthly net gain since mid-2009, before the big Canterbury quake sparked a rush of people leaving for Australia.